1. Field of the Invention
The present invention relates to a camera, a data printing device (to be referred to as a data back hereinafter) capable of being mounted on the camera and of printing various data on a film loaded in the camera, and a film winding device assembled in the camera.
2. Related Background Art and Objects of the Invention
In a camera system in which a camera and a data back which does not communicate data with the camera are combined to perform a photographing operation, the data back changes a data printing time in accordance with a data printing signal from the camera, a transmission time of which changes depending on a film sensitivity. In this system, since signal processing of the data back is not complicated, if the transmission time of the data printing signal transmitted from the camera to the data back changes, no problem is posed.
There is also known a camera system in which a camera and a data back which communicates data with the camera are combined to perform a photographing operation. A camera system of this type which has various functions realized by serial data communication between a camera and a data back is disclosed in Japanese Patent Laid-Open (Kokai) No. 61-167934.
In this system, since signal processing of the data back is complicated, if the transmission time of the data printing signal transmitted from the camera to the data back changes, an erroneous operation may be caused by the change in transmission time.
It is a first object of the present invention to provide a camera which can prevent an erroneous operation when a camera and a data back which does not communicate data with the camera are combined or when a camera and a data back which communicates data with the camera are combined.
Certainly usually inexpensive, data backs having a data communication function may also present a problem related to frame speed. Such data backs typically employ a relatively low speed microcomputer operating on the basis of oscillation at 32 kHz. By contrast, a microcomputer used in a camera requires high-speed processing, for which an oscillator of 4 to 8 MHz is commonly employed. When data communication is to be performed between the microcomputers, the data communication speed must be determined in correspondence with the microcomputer having the lower data communication speed. Since a data communication time is about several tens of ms (although it varies depending on the number of data), frame speed tends to decrease, thus posing a problem. Of course, the microcomputer of the data block may be operated at a clock of about 4 to 8 MHz when the camera is activated, and may be operated at a clock of about 32 kHz when the camera is deactivated. However, in this case, the system becomes complicated, or an expensive microcomputer must be used.
It is therefore a second object of the present invention to provide a camera system in which an inexpensive data back, for example, can perform printing based on data received from a camera without adversely affecting frame speed.
Another significant problem associated with the use of data backs occurs when a data back is combined with a conventional camera having an electric winding device. Such a camera is designed to perform a film winding operation immediately after exposure of an object for a preset shutter time is completed. In order to avoid blurring of the data printed by the data back when the film is wound, the data printing operation is interrupted when the exposure is completed, before the film winding operation is performed. This operating sequence, while avoiding blurring of the printed data, gives rise to another problem when low-sensitivity film is used. More particularly, because low-sensitivity film necessitates along printing time, the print density obtained when the printing operation is interrupted is often insufficient for the data to be discriminated. This phenomenon becomes more pronounced with decreasing shutter time and decreasing film sensitivity.
It is a third object of the present invention to solve this problem.